1. Field of the Invention
The present invention relates to a rubber-coated gasket material having a rubber layer formed on one or both sides of a metal sheet. Gaskets worked from this material not only have a sealing capability but also are adapted for use under hostile conditions such as those where repeated impact and abrasion are exerted by other parts.
Rubber-coated gasket materials contemplated by the present invention are fabricated by punching or stamping desired shapes out of sheeting having a rubber coat formed on the surface of a metal substrate such as a sheet of cold-rolled steel, stainless steel or aluminum. The so fabricated materials are used as gaskets in various apparatus and machines. Because metal sheets are used as substrates, the rubber-coated gaskets will not allow any leakage of the internal gas under pressure. In addition, the elasticity of the rubber layer enables the gasket to closely fit the irregularities which may be found in the surface of a flange and thereby insures reliable sealing properties.
Attempts have been made to furnish a single gasket with more than one capability, for example, a sealing capability plus the ability to work as a stopper of the lead in a lead valve, and such a gasket is inevitably used under hostile conditions, i.e., the rubber coated surface is repeatedly struck or abraded with a metallic or resin lead.
The structure of a rubber-coated gasket material of the type contemplated by the present invention is shown in cross section in FIG. 1. A prior art process for producing such a gasket material is described in U.S. Pat. No. 2,957,784 and comprises a plurality of steps. First, a metal sheet 1 is degreased and then roughened by a suitable technique such as shot blasting or Scotch brightening. A chemical conversion coating 2 is then formed on the metal surface. A primer coating 3 is then formed as an adhesive layer by applying a primer based on a phenolic resin. The primer layer 3 is then coated with a given thickness of a rubber solution which is a mixture of nitrile rubber with a reinforcing carbon black filler, as well as a curing agent and other additive commonly used in rubbers. The coating solution is then dried and cured to form a rubber layer 4. Finally, depending upon the operating conditions of the gasket, a nonsticky layer 5 is formed on the rubber layer 4 by coating a dispersion of graphite, molybdenum disulfide, etc.
The prior art rubber-coated gasket material described above exhibits good sealing properties (e.g. high resistance to oils and chemicals) since nitrile rubber is used as a polymer in the rubber layer 4 formed on the phenolic resin based primer layer 3. On the other hand, mechanical aspects of the gasket performance including strength and has wear resistance have not been considered very seriously in this prior art product, so that if the gasket is of a type that is to be subjected to repeated impact and abrasion by the lead of a lead valve, the strength of the rubber layer 4 itself and the adhesion between this rubber layer and the primer layer 3 are insufficient to prevent the occurrence of cracking in the rubber layer 4 and blistering between the rubber layer 4 and the primer layer 3.